In the related art, a copper alloy such as Cu—Zn has been used for various uses such as a connector, a terminal, a relay, a spring, and a switch which are constituent parts of an electric and electronic apparatuses, a construction material, daily necessities, and a mechanical part. In the connector, the terminal, the relay, the spring, and the like, a copper alloy raw material may be used as is, but plating of Sn, Ni, and the like may be carried out due to discoloration and a corrosion problem such as stress corrosion cracking. Further, even in a use for a metal fitting or a member for decoration and construction such as a handrail and a door handle, and a use for a medical instrument, it is demanded for the discoloration to be less likely to occur. To cope with the demand, a plating treatment such as nickel and chromium plating, resin coating, clear coating, or the like is carried out with respect the copper alloy product so as to cover a surface of the copper alloy with the resultant plating or coating.
However, in the plated product, a plating layer on the surface is peeled off due to use for a long period of time. In addition, in a case of manufacturing a large quantity of products such as connectors or terminals at a low cost, in a process of manufacturing a sheet that becomes a raw material of the products, plating of Sn, Ni, and the like is carried out in advance on a sheet surface, and the sheet material may be punched and used. Plating is not formed on a punched surface, and thus discoloration or stress corrosion cracking is likely to occur. In addition, Sn or Ni is contained in the plating and the like, and recycling of the copper alloy becomes difficult. In addition, the coated product has a problem in that a color tone varies with the passage of time, and a coated film is peeled off. In addition, the plated product and the coated product deteriorate antimicrobial properties (sterilizing properties) of the copper alloy. In consideration of the above-described situation, a copper alloy, which is excellent in the discoloration resistance and the stress corrosion cracking resistance and which can be used without plating, is preferable.
Examples of a use environment when assuming a terminal, a connector, and a handrail include a high-temperature or high-humidity indoor environment, a stress corrosion cracking environment containing a slight amount of nitrogen compound such as ammonia and amine, a high-temperature environment such as approximately 100° C. when being used at the inside of automobiles under the blazing sun or a portion close to an engine room, and the like. To endure the environment, it is preferable that the discoloration resistance and the stress corrosion cracking resistance are excellent. The discoloration has a great effect on not only exterior appearance but also antimicrobial properties or conductivity of copper. A handrail, a door handle, a connector, or a terminal that is not subjected to plating, a connector or a terminal and a door handle in which a punching end surface is exposed, and the like have been used widely, and thus there is a demand for a copper alloy material having excellent discoloration resistance, and stress corrosion cracking resistance. On the other hand, high material strength is necessary in a case where a reduction in thickness of a material is demanded, and is necessary to obtain a high contact pressure when being used for a terminal or a connector. When the copper alloy material is used for a terminal, a connector, a relay, a spring, and the like, the high material strength is used as a stress that is equal to or less than an elastic limit of the material at room temperature. However, as a temperature in a use environment of the material becomes higher, for example, as the temperature becomes as high as 90° C. to 150° C., the copper alloy is permanently deformed, and thus it is difficult to obtain a predetermined contact pressure. To utilize high strength, it is preferable that the permanent deformation is small at a high temperature, and it is preferable that the stress relaxation characteristics, which are used as a criterion of the permanent deformation at a high temperature, are excellent.
In addition, as a constituent material of an electrical part, an electronic part, an automobile part, and a connector, a terminal, a relay, a spring, and a switch which are used in a communication apparatus, an electronic apparatus, an electrical apparatus, and the like, a highly conductive copper alloy with high strength has been used. However, recently, along with a reduction in size, a reduction in weight, and higher performance of the apparatuses, the constituent material that is used for the apparatuses is demanded to cope with a very strict characteristic improvement, or various use environments. Further, excellent cost performance is demanded for the constituent material. For example, a thin sheet is used at a spring contact portion of the connector, and a high-strength copper alloy, which constitutes the thin sheet, is demanded to have high strength, high balance between strength and elongation or bending workability for realization of a reduction in thickness, and discoloration resistance, stress corrosion cracking resistance, and stress relaxation characteristics for endurance against a use environment. In addition, the high-strength copper alloy is demanded to have high productivity, and excellent cost performance, particularly, by suppressing an amount of a noble metal copper that is used as much as possible.
Examples of the high-strength copper alloy include phosphorus bronze that contains Cu, 5% by mass or greater of Sn, and a slight amount of P, and nickel silver that contains a Cu—Zn alloy and 10% by mass to 18% by mass of Ni. As a general-purpose high-conductivity and high-strength copper alloy excellent in cost performance, brass, which is an alloy of Cu and Zn, is typically known.
In addition, for example, Patent Document 1 discloses a Cu—Zn—Sn alloy as an alloy satisfying the demand for high strength.